Wire harnesses or cables which pass through panel openings, for example from the engine compartment of an automobile through the dash panel or fire wall to the passenger compartment, often require a tight seal between the panel and cable to prevent leakage of water and/or fumes between compartments separated by the panel. It is frequently desirable that the seal also provide support for the cable relative to the panel and hole through which it passes, to protect it from abrasion. Finally, the seal should effect a secure and easily-established connection to both the cable or wire harness and the panel.
Several attempts have been made in the prior art to provide a seal assembly which meets the above requirements for automotive panel applications. A first prior art device is a one-piece, all-rubber grommet with an elastic, cylindrical stem which must be forcibly stretched open to axially insert the cable through the grommet. When relaxed the relatively long stem seals tightly against the cable. The body of this one-piece rubber grommet has a peripheral slot or groove for mating it to suitable connecting structure around an opening in a dash panel after the grommet has been fastened to the cable. The stretching operation and installation of the grommet onto the panel both require substantial effort.
A second prior art device combines a rigid support with the rubber grommet seal for an improved snap-fit to the dash panel opening with beveled locking tabs. This device, however, still requires the undesirable stretching operation to axially apply the rubber grommet seal to the wire cable.
U.S. Pat. No. 3,836,269 to Koscik attempts to solve the problems inherent in axial assembly of the grommet to the cable by splitting a grommet assembly into two halves which are hinged to one another. These two hinged halves can accordingly be assembled radially over the cable, rather than axially. The assembled grommet and cable are then inserted into the hole in the dash panel in sealing fashion.
While the Koscik device improves the ease of fastening the grommet around the cable, the seal between the grommet assembly and the cable is significantly less effective and reliable than the seal provided by the rubber, axially-assembled grommets described above. The axial rubber grommets provide a relatively long, elastic stem which, once stretched over the cable and released, provide a large sealing surface relative to the cable. The natural radial tension of the undersize cylindrical stem further improves the effectiveness of the seal with the cable. In the Koscik device, however, the hinged halves and their flanged cable-engaging openings, which form a tubular cable path for the grommet when the halves are folded together, are made from a rigid, non-sealing plastic. For a seal between the grommet assembly and the cable, Koscik relies on an O-ring type gasket, also hinged, with interior cable-sealing ring portions. This hinged gasket is secured to the rigid halves of the grommet assembly with adhesive.
This small, hinged O-ring gasket provides a relatively weak and unreliable seal with the cable, first because any irregularity in the cable cross-section at the interface of the O-ring prevents a seal from being formed, and second because the effective axial length of the sealing surface is small. Additionally, the seal between the edges of the hinged O-ring gasket, when folded together, is not particularly strong.